Glow plug

Abstract

A glow plug (1) including a heater (2), a metallic shell (4) assuming the form of a tube having an axial bore, a center shaft (3) and a contact member (7). The contact member (7) is configured such that a contour (70) of a cross section (75) includes a second contour segment (71) in the form of a straight line, a first contour segment (72) in the form of a curve swelling radially, and third contour segments (73) in the form of curves connecting the second contour segment (71) and the first contour segment (72).

Description

TECHNICAL FIELD[0001]The present invention relates to a glow plug used for assisting in start-up of a diesel engine.BACKGROUND ART[0002]A glow plug used for assisting in start-up of a diesel engine is such that a heater which has a heat-generating resistor at its forward end portion is held directly or indirectly at a forward end portion of a tubular metallic shell having an axial bore. A rodlike center shaft is inserted into the axial bore of the metallic shell and disposed in a condition electrically insulated from the metallic shell. One end portion of the center shaft is connected to a rear end portion of the heater, and the other end portion projects from the rear end of the metallic shell. Two electrodes led from the heater are electrically connected to the metallic shell and the center shaft, respectively.[0003]In the thus-configured glow plug, in order to ensure gastightness through the axial bore of the metallic shell, an O-ring is disposed between the center shaft and the ...

AI Technical Summary

Benefits of technology

The patent relates to a glow plug used in automobiles and the invention is a new design for the contact member that reduces friction and prevents twisting of the O-ring during assembly. The contact member is designed to have a contact area with the shoulder portion of the glow plug that is small to prevent the contact member from being caught and dragged inward. This results in a more stable attachment of the contact member to the glow plug and reduces the risk of failure during use.

Problems solved by technology

However, in the configuration in which the three contact surfaces of the inner circumferential surface, the center shaft, and the insulation member surround the O-ring, difficulty is encountered in providing a space for accepting deformation of a compressed O-ring.

Accordingly, the O-ring is deformed in such a manner as to enter a narrow gap between the contact surfaces; thus, internal stress in a deformed portion of the O-ring increases, potentially resulting in breakage of the O-ring.

Accordingly, the O-ring fails to maintain sufficient close contact with the contact surfaces; thus, a clearance is formed therebetween, potentially resulting in a failure to ensure gastightness.

In the process of assembling a glow plug, when the O-ring is to be disposed in a narrow gap between the center shaft and the inner circumferential surface of the axial bore, there has been involved the risk of twist of the O-ring along the circumferential direction.

Joint use of an axially long tube-like vibration insulating rubber or the like encounters difficulty in disposition between the center shaft and the inner circumferential surface of the axial bore and increases cost.

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